For the same person directly supported by level ground in each posture, assume…

Concept

Average pressure is the normal force acting per unit contact area. For a stationary person on level ground, p = F/A, and the total normal force is approximately the person’s weight.

For the same person, posture does not change the total weight; it changes the effective area through which that force reaches the ground.

Application

1. Use the same person in all three cases, so the force F is fixed at approximately mg.

2. The stem defines the standing contact as two soles, the sitting contact as the buttocks and legs, and the lying contact as the back and limbs; it also states that their effective areas increase in that order.

3. Thus, two soles provide the smallest stated effective contact area. With F fixed, p = F/A is largest for the standing posture.

Contrast

• Sitting position: the buttocks-and-legs contact region is larger than the two-sole region.

• Lying position: the back-and-limbs contact region is the broadest of the three.

• More than one of the above: a tie would require at least two defined contact areas to share the minimum value.

• None of the above: this would mean no listed posture produces the greatest average pressure, whereas a strict area order with fixed force necessarily gives one listed posture the maximum.

Cross-check

Keeping F fixed and increasing A lowers F/A, while decreasing A raises it. The stated direct-ground contact conditions remove chair, tiptoe, one-foot, and external-support variations from the comparison.

Result

Therefore, the standing position produces the greatest average pressure on the ground under the stated conditions.